Lol i agree. Tail bitters are crazy. You never know when they will do it again. I am lucky one of my betta did it may be 6 times in his life. He is almost 3 years old. But again i like to do more frequent water changes because it scares me when i see literally half of his tail bitten. I know a lot of people recommending to use stress coat, but so far my betta didn't get any infection yet.

I kind of think he started when I added a few ghost shrimp into the tank...but he really doesn't seem to mind them, especially now that he's realized he can steal food from them, lol! So hopefully it was just a tiny bit of stress from that and now he's over it...fingers crossed.

I forgot to ask. You wrote that they flaring at each other at night when their light is on but the room light is off. I don't think you need to keep light in the tank at night. This way you will resolve the problem and also i think it can be stressful if you keep light all the time.

Their tank light is on from about 7am to 10pm most days. If I have the day off, I sleep in and it doesn't go on until about 9am or so. I don't mind turning the light off a little earlier in the evening but I like to watch them and I can't see them otherwise since it gets dark so early now! :(

I read that in most cases they will stop after a couple of days as they get used to their new surroundings. Occasional flaring i guess is normal and healthy behavior. If he still flares and get stressed

Often the easiest fix is to adjust the light. The reflection is caused by the angle at which the light is hitting the glass. Often turning the tank or moving it to another location will fix the problem. Also , the background color outside the aquarium can enhance or reduce his ability to see his reflection. Darker colors show the reflection more than light colors. Keeping the tank away from walls or nearer light colored walls will be better then keeping it against a dark wall. Most fish stores carry aquarium backdrop images you can tape to the outside of the tank. While a solid blue or black backdrop will worsen the reflections,images of aquarium plants or rocks will hide the reflection..
Adding live or silk plants is a great way to break up th sightlines between your betta and his reflection.

Thanks for the good info! They don't seem to be constantly flaring, just more than usual...maybe because I am doing more water changes and they are feeling happier? I do have a backdrop and lots of plants in my tank - they seem to only flare in the front of the tank, so maybe they are just showing off for me when I'm watching them? Unfortunately my light isn't bright enough for more live plants, and it is not replaceable unless I get a whole new hood which I don't really want to buy. I bought a kit at Walmart with an LED light, and it's great but the light could be better.